The trolls on social media are at it again. This time they're criticising the casting of a black actress to play Hermione in the new stage play Harry Potter and the Cursed Child.

It was announced this week that Swaziland-born actress Noma Dumezweni,45, would play the adult version of the role made famous by Emma Watson when the show premieres on London's West End in June.

While some of the haters have posted openly racist comments, Harry Potter scribe JK Rowling has come out in defence of the casting, saying she "loves black Hermione".

If fact, as described by JK in her own work, Hermione sounds like she might have more in common physically with Noma than with Emma.

Take that, haters.

The stage version of Harry Potter is set 17 years after the end of the seventh instalment of the book series. Jamie Parker will play adult Harry Potter, while Paul Thornley will be a grown-up Ron Weasley.

Though neither Jamie nor Paul have much in common with the original Harry and Ron - Daniel Radcliffe and Rupert Grint, repsectively - it's the casting of Nona that's stirring the controversy pot.

Though she's not a name actress, Nona has impressive credentials. She's currently playing the lead in a London production of Linda, after replacing Kim Cattrall in the role (yes, that's Sex and the City's Samantha).

She has also excelled at roles written specifically for a black actress, having won a 2006 Olivier award for her supporting performance in a stage production of A Raisin in the Sun.

If the Harry Potter reviews are good and the ticket sales are strong, does it matter how Hermione looks? Clearly the majority of ticket buyers are unconcerned. The show set a West End record by selling 175,000 tickets in one day.